Lubricant coating composition and method of cold forming metals



Unitd Ste 3,12,61 LUBRECANT CfiATlNG (IUIVEGSETHUN AND METHGD 8F 69M) FGPJr HNG METALS Werner Hansel: and Wolfgang Wutthe, Frankfurt am Main, Germany, and Eberhard Eohres, Detroit, Mich assignors to Hooker (Zhernicai (Iorporation, Niagara Falls, N.Y., a corporation of New Yuri No Drawing. File-l June 8, 13362, Ser. No. 2%,912 Claims priority, application Germany, June 13, 196i, M 49,332 11 Saints. (6i. 29-424) The present invention broadly relates to lubricant coatings for facilitating the noncutting cold forming of metals and more particularly to an improved resinous coating comprising a cellulose ether based resin which provides improved cold forming characteristics without discoloring the surface of the metal being formed and to a method of cold forming metal employing a coating of such composition.

A variety of materials have heretofore been used or proposed for use in connection with the noncutting cold forming of metals to facilitate deformation or size reduction of the metal being Worked so as to minimize friction between the die and workpiece reducing surface scoring and minimizing rupture or fracture of the metal being formed. A large number of inorganic and organic lubricant materials have heretofore been employed individually or in mixtures for facilitating such cold forming operations. Further improvements in the lubricity characteristics of such inorganic and organic lubricants have been obtained by employing phosphate layers, for example in connection with iron, steel, aluminum and zinc metals or oxalate layers, for example, in connection with cold forming of fine steel which provide improved retention of such lubricants applied to the surfaces enabling greater individual or total reduction or deformations per pass than was possible by employing such lubricants in the absence of such phosphates or oxalate layers.

While the use of such binding layers in combination with organic and inorganic lubricants has provided a substantial improvement in cold forming operations, the use of such phosphate or oxalate layers, for example, produce an undesirable light gray, dark gray or greenish discoloration of the metallic surface of the metal being formed. Such a discoloration is particularly disadvantageous when metallic bright surfaces are desired on the finished cold formed metal workpiece. In such case it is necessary to remove the discoloration by subjecting the formed workpieces to further degreasing and acid or alkaline treating steps to remove the lubricant layer from the surfaces thereof. Such subsequent cleaning operations constitute a costly and time-consuming operation detracting from the improved lubricity characteristics which such coatings provide.

It is accordingly, a primary object of the present invention to provide a new lubricant coating composition and an improved method for cold forming metal workpieces which overcomes the problems and disadvantages associated with lubricity coatings of the type heretofore known.

Another object of the present invention is to provide an improved lubricant coating and an improved method for cold forming metal articles which substantially reduces the friction between the metal and forming die during cold forming operations eliminating surface scoring Patented July 6, P955 and so-called die chattering while concurrently providing a finished article which retains its original bright metallic finish obviating the necessity of subjecting the finished workpiece to further intensive cleaning and treating operations to remove surface discolorations therefrom as frequently encountered in lubricant coatings heretofore known.

Still another object of the present invention is to provide an improved lubricant coating and method for fa cilitating the cold forming of metallic articles which does not impart an undesirable discoloration to the metallic bright surfaces and which simultaneously provides for exceptional lubricity characteristics enabling the metal to be formed to be subjected to a greater number of forming or sizing cycles without rupture, fracture or surface scoring than is possible with lubricant coatings heretofore known.

A further object of the present invention is to provide an improved lubricant coating and method for cold forming metals which is simple and economical to manufacture, use and remove providing for increased eiiiciency, material handling and disposal problems in comparison to those encountered employing lubricant coating compositions of the types heretofore known.

The foregoing and other objects and advantages of the present invention are based on the discovery that surprisingly superior lubrication characteristics are provided by cellulose ether base coatings applied to the surfaces of metals to be cold formed in amounts based on the weight of the dry film of from about 1 gram per square meter (about 93 milligrams per square foot) to about 15 grams per square meter (1394 milligrams per square foot). The cellulose ether base resin coating may be conveniently applied to the metallic surfaces subjected to contact with the forming or sizing die by forming a solution or dispersion of the resin in a volatile solvent preferably of a concentration greater than about 20% by weight. In addition to the cellulose ether resin, suitable modifying agents may also be incorporated in small proportions such as modifying resins, softening agents, phosphate compounds, inorganic pigments and the like to provide optimum adhesion characteristics and strength of the coating enhancing its lubricity characteristics for any particular cold forming operation. The improved lubricant coating can be employed alone or in combination with other suitable lubricant coatings applied to the exterior surface of the resultant dried film which, in some instances provide still further improvement in the cold forming characteristics thereof.

In accordance with the method comprising the present invention, the improved lubricant coating composition can be employed in connection with the cold forming of all types of metals and the advantages derived therefrom are particularly pronounced in the cold forming of metals such as fine steel, nickel-chromium alloys, titanium, zirconium, for example, which are conventionally difficult to form. The coating composition is also particularly desirable for facilitating difficult cold forming operations such as the drawing of tubes with large outlets, cold flow stampings and deep drawing with reductions of the wall thickness. In all cases, however, the method employing the improved lubricant coating provides for substantial advantages in comparison to that obtained from lubricant coatings of the types heretofore known.

Cellulose ether based resins suitable for use in forming the lubricant coating on metallic surfaces include methyl cellulose, ethyl cellulose, oxyethyl cellulose, ethylhydroxyethyl cellulose, benzyl cellulose and the like. Of the foregoing cellulose ethers, methyl cellulose has the further advantage of being soluble in cold water as well as in organic solvents. In comparison, the remaining cellulose ether resins are insoluble in water in the concentrations conventionally employed necessitating the use of suitable organic solvents.

Any one of a number of suitable organic solvents can be satisfactorily employed for forming a solution or dispersion of the cellulose ether base resin preferably in con centrations of more than about 20% by weight and particularly in concentrations of greater than about 35% by weight. Organic solvents which can be suitably employed include chlorinated hydrocarbons such as methylene chloride, trichlorethylene and perchlorethylene; alcohols, esters, ketones, aromatic hydrocarbons and the like. Of the foregoing solvents, chlorinated hydrocarbons are frequently preferred because of their non-infiammability reducing any fire hazard associated with their use. The solvents can be employed individually as well as in mixtures in order to provide a stable, compatible solution or dispersion of the resin constituents.

The particular concentration of the resin constituent in the solution or dispersion will vary somewhat depending on the particular viscosity of the coating composition as well as on the method employed for applying the composition to a metal surface. conventionally, the concentration is adjusted so as to provide a substantially dry resin film on the metal surface of from about 1 gram to about 15 grams per square meter (about 93 to about 1395 milligrams per square foot). Film coatings less than about 1 gm./ sq. meter generally do not provide a thickness suf ficient to produce the requisite reduction in friction to facilitate cold forming as is provided by employing amounts greater than about 1 gm./sq. meter. On the other hand, film layers in excess of about 15 gm./sq. meter do not particularly increase the cold forming characteristics of the metal in comparison to that provided by layers present in an amount of about 15 grams and, accordingly, is economically undesirable. Moreover, lubricant layers applied in amounts in excess of about 15 gm./sq. meter in some instances create problems during cold forming operations and particularly in drawing operations whereby an excess accumulation of resin film occurs in the drawing die. It is for these reasons that it is conventionally preferred to control the quantity of the resin film on the metal surface to within an amount ranging from about 1 up to about 15 gm./ sq. meter.

In addition to the cellulose ether resin constituent, the lubricant coating composition may also incorporate small proportions of various modifying agents in amounts sufficient to enhance the lubricant characteristics of the coating which is desirable in some instances for achieving optimum cold forming characteristics consistent with a particular type of cold forming operation. Accordingly, it is sometimes desirable to incorporate suitable modifying resins such as polychloroprene, fatty acid modified alkyd resins, polybutenes, polyethylene and the like. In addition, suitable softening agents can be employed for controlling the hardness of the resultant dried film such as, for example, dioctyl sebacate and trichlorethyl phosphate. Suitable natural and/or synthetic waxes, fatty acids such as, for example, stearic acid and coco oil fatty acid, fatty acid alkanolamides such as, for example, monocthanolamide of coco oil fatty acid; animal and/or plant or vegetable fats such as for example, tallow, wool fat and colza oil; polyvinylalkyl others such as, for example, polyvinylisobutyl ether can also be incorporated either individually or in admixture in amounts effective to improve the particular cold forming characteristics of the coating in accordance with a particular cold forming operation. I

The addition of small quantities of the aforementioned Al modifying agents such as, for example, polyvinylalkyl ethers, the softening agents, the fatty acids and the fatty acid modified alkyd resins also provide for increases in the adhesive strength of the cellulose ether film on the metal surface.

The aforementioned addition agents are conventionally included in the lubricant coating formulation in amounts sufiicient to provide an effective improvement in the desired lubricant characteristics which generally range from up to about a quantity equal to the cellulose ether resin constituent in the coating composition and more usually in amounts ranging from about 10% up to about 25% of the cellulose ether constituent present. Improvements derived as a result of the incorporation of small proportions of such modifying agents will become apparent in accordance with the test results obtained on typical formulations as set forth in Example II which will be subsequently described in detail.

In addition to the foregoing modifying agents, suitable solid additives or pigments such as graphite, talcum, molybdenum disulfide, chalk, kaolin and the like can also be added to the lubricant coating composition in order to increase the firmness of the resultant dry film. Such solid additives, however, are employed only in the case of extremely difficult cold forming operations since the use of such additives make it diflicult to remove the residuary film after the cold forming operation from the metal article. Conventionally, it is necessary to employ relatively intensive aftercleaning treatment to remove such films containing solid pigment additives which detracts from the advantages of employing cellulose ether base coatings which are extremely simple to use and remove.

In lieu of or in combination with the use of solid additives in the lubricant coating for difiicult cold forming operations, the coating formulation can be further modified by incorporating small quantities of phosphoric acid and/or phosphoric acid esters in the resin solution or dispersion which produces a clear phosphate layer on the coated metal surface and increases the adherence of the coating on the base metal. The organic portion of the phosphoric acid ester preferably comprises a fatty alcohol having a chain length ranging from about Cg to about C The lubricant coating can be simply prepared by dissolving or dispersing the appropriate proportions of a suitable cellulose ether base resin in a solvent system so as to provide a concentration greater than about 20 grams per liter and preferably greater than about 35 grams per liter. In addition, appropriate proportions of suitable modifying agents and/ or additives may be incorporated if desired to further improve the cold forming characteristics of the coating consistent with a particular cold forming operation. The lubricant coating formulation is preferably applied in the form of a substantially uniform layer at room temperature and can be applied by any one of the techniques well known in the art such as, for example, immersion, flooding, pouring over, spraying and the like. The metal surface to be coated is preferably cleaned by any one of the techniques well known in the art so as to remove therefrom any undesirable contaminating materials such as grease, dust, corrosion products and the like which might otherwise interfere with achieving good adhesion of the coating to the metal's'urface.

After the lubricant coating composition is applied, the coated metal workpiece is allowed to dry either at room temperature or at an elevated temperature so as to remove substantially all of the solvent therefrom. As hereinbefore set forth the resultant dried film is controlled so as to be present in an amount ranging from about 1 gm./ sq. meter (93 mg./sq. ft.) to about 15 gm./sq. meter (1394 mg./ sq. ft,). In this condition the metal can thereafter be subjected to the cold forming operation with or without the additional use of lubricants on the lubricant coating. In some cases such additional conventional lubricants provide for further improvements in the cold forming characteristics of the lubricant coating and the use thereof in such instances is preferred. For example, the use of suitable greases and/or mineral oils as applied over the dried lubricant coating facilitates removal of the formed metal sheet from the dye during deep drawing operations.

At the completion of the cold forming operation, the residuary lubricant coating and any secondary lubricants applied thereover if used can be simply removed from the surfaces of the cold formed metal articles by employing suitable organic solvents or through the use of a solvent-steam cleaner, for example.

The surface of the metal article cold formed and cleaned in this manner is distinguishable from that obtained by lubricant coatings heretofore known in that the surface is characterized as being substantially devoid of any grooves or score lines and being splotlessly clean. As a further advantage of the lubricant coating and the method of cold forming metals comprising the prevent invention, the exclusive use for organic solvents for applying and removing the coating in combination with scale-free annealing of the cold hardened parts under a protective gas atmosphere results in the complete elimination of contaminated treating liquors which conventionally require extensive purification providing therewith a significant advantage in overcoming sewage disposal problems.

In order to further illustrate the lubricant coating composition and method of cold forming metals employing the composition, theh following examples are provided. It will be understood, however, that these examples are intended to illustrate typical suitable formulations of the lubricant coating formulation and the advantages derived through the use thereof and are not intended to be limiting of the scope of the present invention as set forth in the subjoined claims.

EXAMPLE I In order to illustrate the surprisingly superior cold forming characteristics of the lubricant coating comprising the present invention containing a cellulose ether resin over that obtained by other synthetic organic resins, a series of comparative tests were conducted employing a typical coating composition of the present invention and a series of synthetic resins of the types well known in the art. In each case the films of synthetic resins as well as the cellulose ether resin were applied from solvent solutions on the surfaces of bright steel tubes. The weight of dry film was controlled in each case to an amount of about grams per sq. meter (929 mg./sq. ft.). After each of the films were dried by vaporization of substantially all of the solvent therefrom, the tubes were drawn through a die under substantially equal conditions at a drawing velocity of 7 meters per minute (about 23 ft. per min.).

The size reduction drawing operation of the steel tubes was accomplished by employing a series of drawing dies of progressively decreasing diameter effecting a progressive reduction in the outside diameter and wall thickness of the tube during each drawing pass. The specific reduction in outside diameter and wall thickness of the using for each pass is as follows:

Table 1.Tube drawing operation The number of possible drawings made before surface scoring or cracking or fracture of the tube walls occurred 6 for each of the coating compositions tested are listed in Table 2.

Table 2.-Comparative results Number of Drawings Possible Before Encountering Scoring or Tube Cracking Coating Composition NNWLOMHHIOMNUQG The comparative drawing characteristics of the various resin films was made without the use of additional lubricants applied to the surfaces of the dried films. It is apparent from the comparative results obtained on the several coating compositions as set forth in Table 2 that coating compositions employing cellulose ether resins of the type comprising the present invention are surprisingly superior in comparison to the lubricating characteristics provided by the remaining synthetic resins tested. In accordance with these data, it is apparent that generally 5 or more drawings can be obtained when employing lubricant coatings of a cellulose ether resin as typified by the coatings of methyl cellulose, ethylhydroxyethyl cellulose, and ethyl cellulose designated as l, 2, and 3, respectively, in Table 2, in comparison to a maximum of three drawings by the use of alternate synthetic resin coatings and more usually only two or only one drawing pass during which scoring and die chattering occurred. In this latter regard, a great deal of die chattering and shrieking occurred during the drawing of tubes coated with synthetic resins of the types designated as 4 through 13 which is extremely objectionable. In comparison the lubricant coating prepared in accordance with the present invention and typified as the coatings numbered 1-3 inclusive in Table 2, resulted only in intermittent soft die chattering which was audible for only short periods of time.

EXAMPLE 11 To further illustrate the improved cold forming characteristics of the coating comprising the present invention as further modified by incorporating therein suitable modifying agents of the type hereinbefore set forth, a second series of experiments were conducted employing various modifying agents in the cellulose ether base resin formulation. The cold forming characteristics were determined by tube drawing operations of the same type as previously described in Example I. The bright steel tubes were coated with the several coating compositions by immersion followed by air drying in the same manner as the coatings previously described in connection with Example I. The weight of the dry film deposited on the tube surfaces ranged from about 6 grams per sq. meter to about 12 grams per sq. meter (about 558 to about 1116 mg./sq. ft.). The several coating solutions were prepared by dissolving the various modifying agents in a solution of ethyl cellulose dissolved or dispersed in a solvent system consisting of equal volumes of methylene chloride and perchloroethylene.

The particular composition and amount and type of addition agents employed as well as the number of possible drawings which could be made before effecting surface scoring or cracking of the tube are set forth in Table 3.

Table 3.-Cmparativc results of modified cellulose other base coatings Number of the Coating Composition (gnL/l) Possible Drawings Before Scoring or Ethyl Modifying Agent Cracking of Cellulose the Tube 1 60 N one 2-. 60 12 (all)ryd resin modified with fatty 7 a o 3 60 12 (triehlorothyl phosphate) 7 4- 60 12 (polybutenc) 7 6D 12 (polyethylene molar weight 250 7 6. 60 12 (dioctylscbacatc) 7 30 (polyvinylisobutyl ether) 7 8. 30 (polychloroprcnc) 7 12 (stearic acid) 7 10 (30 12 (coco oil fatty acid) 7 It will be apparent from the comparative data as set forth in Table 3 that each of the modified coatings enabled 7 reduction passes of the tubing through the reduction dies without encountering any scoring or tube cracking. In the case of the coating compositions indicated 1-3 inclusive in Table 3, a soft die chattering occurred intermittently which was audible for only short time periods. The remaining coating compositions provided for absolutely quiet drawing operations which is particularly desirable from the standpoint of the working environment. It should be further pointed out that the coating composition designated 4 in Table 3 containing 12 rams per liter of polybutene was in the form of a dispersion of the polybutene in the solvent system containing the ethyl cellulose EXAMPLE III An additional coating formulation was prepared which is representative of one containing a phosphate compound which is particularly desirable in the case of extremely difficult cold forming operations. The composition of the coating formulations is set forth in Table 4.

Table 4.Ph0sphate modified coating composition Ingredient: Amount Ethyl cellulose grn./l 60 Dioctyl sebacate grn./l 12 Phosphoric acid gm./l 30 Solvent:

Methylene chloride liter" .4 Perchlorethylene do .4 Isopropanol do .2

The coating was applied to steel tubes in the same manner as previously described in Example I and subjected to a series of drawing operations as hereinbefore described providing absolutely quiet drawing without any die chattering and enabling seven reduction passes without any evidence of surface scoring or fracture of the tubes.

While it will be apparent that the preferred embodiments of the invention disclosed are well calculated to fulfill the objects above stated, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope or fair meaning of the subjoined claims.

What is claimed is:

1. The method for facilitating the cold forming of metals comprising the steps of applying a coating on a metal surface in an amount sufiicient to deposit a substantiaily dry resin film of from about 1 to about 15 grams per sq. meter, said resin in said coating comprising a cellulose ether selected from the group consisting of methyl cellulose, ethyl cellulose, oxycthyl cellulose, ethylhydroxyethyl cellulose, benzyl cellulose, and mixtures thereof; drying said coating, cold forming the coated metal to the desired configuration, and thereafter removing said coating from the metal surface.

2. The method of facilitating the cold forming of metals comprising the steps of applying a coating comprising a volatile solvent containing at least about 20% by weight of a cellulose ether resin on a metal surface in an amount sufficient to deposit a substantially dry resin film of from about 1 to about 15 grams per sq. meter, drying said coating, cold forming the coated metal to the desired configuration, and thereafter removing said coating from the metal surface.

3. The method for facilitating the cold forming of metals comprising the steps of applying a coating on a metal surface in an amount sufficient to deposit a substantially dry resin film of from about 1 to about 15 grams per sq. meter, said coating composition comprising a volatile solvent and a cellulose ether resin including therein a modifying resin selected from the group consisting of polychloroprene, fatty acid modified alkyd resins, polybutene, polyethylene, and mixtures thereof in an amount sufiicient to provide an improvement in the lubricating characteristics of said coating, drying said coating, cold forming the coated metal to the desired configuration, and thereafter removing said coating from the metal surface.

4. The method for facilitating the cold forming of metals comprising the steps of applying a coating on a metal surface in an amount sufficient to deposit a substantially dry resin film of from about 1 to about 15 grams per sq. meter, said coating comprising a cellulose ether resin in a volatile solvent and a softening agent selected from the group consisting of dioctyl sebacatc and trichlorethyl phosphate and mixtures thereof in an amount sufficient to provide an improvement in the lubricating charactcristics of said coating, drying said coating, cold forming the coated metal to the desired configuration, and thereafter removing said coating from the metal surface.

5. The method for facilitating the cold forming of metals comprising the steps of applying a coating on a metal surface in an amount sufficient to deposit a substantially dry resin film of from about 1 to about 15 grams per sq. meter, said coating comprising a cellulose ether resin in a volatile solvent and a fatty acid modifying agent present in an amount sufficient to provide an improvement in the lubricating characteristics of said coating, drying said coating, cold forming the coated metal to the desired configuration, and thereafter removing said coating from the metal surface.

6. The method for facilitating the cold forming of metals comprising the steps of applying a coating on a metal surface in an amount sufficient to deposit a substantially dry resin film of from about 1 to about 15 grams per sq. meter, said coating comprising a cellulose ether resin in a volatile solvent and a modifying agent selected from the group consisting of natural waxes, synthetic waxes, and mixtures thereof in an amount sufficient to provide an im provcment in the lubricating characteristics of said coating, drying said coating, cold forming the coated metal to the desired configuration, and thereafter removing said coating from the metal surface.

7. The method for facilitating the cold forming of metals comprising the steps of applying a coating on a metal surface in an amount sufficient to deposit a substantially dry resin film of from about 1 to about 15 grams per sq. meter, said coating comprising a cellulose ether resin in a volatile solvent and a fatty acid alkanolamide modifying agent present in an amount sufficient to provide an improvement in the lubricating characteristics of said coating, drying said coating, cold forming the coated metal to the desired configuration, and thereafter removing said coating from the metal surface.

8. The method for facilitating the cold forming of metals comprising the steps of applying a coating on a metal surface in an amount sufficient to deposit a substantially dry resin film of from about 1 to about 15 grams per sq. meter, said coating comprising a cellulose ether resin in a volatile solvent and a polyvinylalkyl ether modifying agent present in an amount sufficient to provide an improvement in the lubricating characteristics of the coating, drying said coating, cold forming the coated metal to the desired configuration, and thereafter removing said coating from the metal surface.

9. The method for facilitating the cold forming of metals comprising the steps of applying a coating on a metal surface in an amount suificient to deposit a substantially dry resin film of from about 1 to about 15 grams per sq. meter, said coating comprising a cellulose ether resin in a volatile solvent and a modifying agent selected from the group consisting of animal oils, vegetable oils, and mixtures thereof present in an amount sufficient to provide an improvement in the lubricating characteristics of said coating, drying said coating, cold forming the coated metal to the desired configuration, and thereafter removing said coating from the metal surface.

10. The method for facilitating the cold forming of metals comprising the steps of applying a coating on a metal surface in an amount sufiicient to deposit a substantially dry resin film of from about 1 to about 15 grams per sq. meter, said coating comprising a cellulose ether resin in a volatile solvent and a finely particulated solid modifying agent selected from the group consisting of graphite, talcum, molybdenum disulfide, chalk, kaolin, and mixtures thereof present in an amount sufiicient to provide an improvement in the lubricating characteristics of said coating, drying said coating, cold forming the coated metal to the desired configuration, and thereafter removing said coating from the metal surface.

References Cited by the Examiner UNITED STATES PATENTS 2,111,342 3/38 Waldeck 117127 2,273,518 2/42 Gloor 117--166 X 2,394,101 2/46 Phillips.

2,588,234 3 /52 Hendricks 113-5 1 2,641,556 6/53 Robinson 117166 X 2,798,009 7/57 Gault 117-127 2,850,999 9/58 Kaplan et a1. 11351 2,871,143 1/59 Getting 117166 X 3,092,523 6/63 Fromson 117-166 X WHITMORE A. WILTZ, Primary Examiner.

RICHARD D. NEVINS, THOMAS H. EAGER,

Examiners. 

1. THE METHOD FOR FACILITATING THE COLD FORMING OF METALS COMPRISING THE STEPS OF APPLYING A COATING ON A METAL SURFACE IN AN AMOUNT SUFFICIENT TO DEPOSIT A SUBSTANTIALLY DRY RESIN FILM OF FROM ABOUT 1 TO ABOUT 15 GRAMS PER SQ. METER, SAID RESIN IN SAID COATING COMPRISING A CELLULOSE ETHER SELECTED FROM THE GROUP CONSISTING OF METHYL CELLULOSE, ETHYL CELLULOSE, OXYETHYL CELLULOSE, ETHYLHYDROXYETHYL CELLULOSE, BENZYL CELLULOSE, AND MIXTURES THEREOF; DRYING SAID COATING, COLD FORMING THE COATED METAL TO THE DESIRED CONFIGURATIONS, AND THEREAFTER REMOVING SAID COATING FROM THE METAL SURFACE. 